Abstract: Xizangite is a tourmalitic volcanic rocks， discovered and nam ed according to its locality by the authors. This is a new type of igne ous rock. As one of the most important rock-forming minerals within xizangite, the tourm aline from xizangite remarkably differs from that of plutonite, metasomatite a nd tourmalinite in occurrence, texture and structure. Based on the macroscop ic and microscopic mineralogical features of studied tourmaline, and the publish ed experimental data derived from studies of granitic system with added boron, t hi s paper suggests that the majority of tourmaline from xizangite was crystallized directly from a suddenly condensing B- and H2O-rich acid magmatic-hydr othermal transitional fluid. However, it bears even more analogy with magma in overall nature, or the washanite magma. While approaching the earth's surfac e, the internal pressure of washanite magma was much higher than the external p ressure and the space was limited. A cryptoexplosion-explosion took place, and tourmaline cemented the breccia together with quartz and crystals-clasts. Durin g washanite magma overflowing tourmaline and quartz could accumulatively crystal lize separately and form the rhythmic “layering structure.”